Under Site Information we can provide custom 404 and 403 pages to Drupal, but these need to be created inside Drupal, and non Drupal pages are rejected. (such as myerror/404.html).

Contrib modules like custom error and static 404 also work inside Drupal. Any ideas on how to set an external page as 404 or 403?

Comments

Help me plz

Try it by editing your .htaccess file by adding:
ErrorDocument 403 /noaccess.html
ErrorDocument 404 /notfound.html

And ofcourse create the page itself ;)